The invention relates to a mid-frame according to the preamble of patent claim 1 and a gas turbine having such a mid-frame.
A mid-frame for a gas turbine is to be taken as known from U.S. Pat. No. 6,763,653 B2, for example. The mid-frame comprises at least one outer casing element, in particular in the form of an outer casing shell, which is designed to be at least essentially ring-shaped, for example. The mid-frame further comprises at least one hub element arranged on the inside of the outer casing element in the radial direction. The hub element is at least essentially a ring-shaped inner structure, for example, which forms or delimits at least partially a hub or a hub chamber or a bearing chamber of the gas turbine. For example, at least one rotor, in particular at least one turbine wheel, of the gas turbine is mounted on the hub element so as to rotate around an axis of rotation relative to the hub element. Here, the rotor, for example, is arranged at least partially in the hub element or in the hub.
The mid-frame further comprises at least one strut, which extends at least essentially in the radial direction, for example. The outer casing element is connected to the inner hub element via the strut. A plurality of such struts, by means of which the outer casing element is connected to the hub element, is usually provided.
Moreover, the mid-frame comprises at least one cladding element, which is usually referred to as a “fairing.” The strut is at least partially clad on the outer peripheral end by means of the fairing element. For this purpose, the fairing element has a passage opening through which the strut passes. In other words, the strut extends through the passage opening in the radial direction.
Moreover, a duct through which a gas can flow is delimited at least partially by the fairing element at least in the radial direction. The gas is a hot gas, for example, so that the duct is also referred to as a “hot-gas duct.” The strut is protected from the hot gas by means of the fairing element, because the hot gas (gas) is conducted around the strut by means of the fairing element and thus cannot flow directly against the strut.
Such a mid-frame is generally employed for multiple-shaft gas turbines. In such a multiple-shaft gas turbine, the duct, constructed as a flow duct that conducts hot gas, is usually arranged between the turbine regions of the gas turbine in the direction of flow of the gas. In a two-shaft gas turbine, a first of the turbine regions is a high-pressure turbine region, for example, while the second turbine region is a low-pressure turbine region. In a three-shaft gas turbine, the flow duct that conducts the hot gas is arranged, for example, between the high-pressure turbine region and an intermediate-pressure turbine region of the three-shaft gas turbine. Alternatively or additionally, such a flow duct that conducts a hot gas is arranged between the intermediate-pressure turbine region and the low-pressure turbine region of the three-shaft gas turbine.
The strut, arranged in the region of the duct, ensures a structural connection of the outer casing element to the hub element and crosses the gas flow. In small gas turbines, the duct is often designed as an integral component. In larger gas turbines, however, a segmented construction design of the duct is provided. In such a segmented construction design, usually a plurality of duct segments, such as, for example, the fairing element, are provided, which are arranged in the peripheral direction of the outer casing element in succession, that is, one behind the other. At least one duct for conducting the gas is delimited at least partially by the respective duct segments.
US 2010/0303610 A1 discloses a mid-frame for a gas turbine, having at least one outer casing element, having at least one hub element arranged on the inside of the outer casing element in the radial direction, having at least one strut, by means of which the outer casing element is connected to the hub element, and having at least one fairing element that delimits at least partially a duct, through which a gas can flow, at least in the radial direction and is constructed separately from the casing element, said fairing element having a passage opening, through which the strut passes, for at least partial cladding of the strut on the outer peripheral side.